Are you having trouble with BTD4? thne this guide might help you.

Step 1 Getting Started:
The 1st Time you're playing you'll only have one weapon which won't be much help in the later levels.

1st Time playing: Get all or most of the weapons
2nd Time playing: Get the rest of the Weapons or Unlock some Level 5 Upgrades
3rd - 4th Time Playing: Unlock the rest of the Level 5 Upgrades

Step 2 Difficulties
Rounds 1-25 Easy: these levels are easy rack up some money and buy a few monkeys or better yet some Banana Farms

Rounds 26-50 Medium: this is when it gets slightly harder if you've got good defenses and it'll introduce you your old friend the MOAB

Rounds 51-75 Hard: This is when things can get interesting you should have at least 1-3 Super Monkeys and at least 3 MOAB Maulers it will also introduce you to the BFB at Round 60

Rounds 76-99 Extreme: Even if your defenses are well put this will put you to the very limit (a ton of BFB's and MOAB's)

Rounds 100+ Impossible: Very few have reached this era of bloons even if you have a lot of Super Monkeys it will still be a challenge and most of these rounds will last at least 30 minutes or longer this will test 150% of your Tower Defense skill(These Rounds take a MASSIVE amount of Luck there will be at least 100000 bloons in each round)

The Last Possible Round is 149 Round 150 is just impossible

Step 3 Know Your Bloons:

Easy Bloons:

Red
Blue
Green
Yellow
Pink

Medium Bloons:
Black (immune to bombs/explosions)
White (immune to Ice)
Camo (use tacks to finish them off easily)
Lead (Immune to anything sharp)
Zebra (Immune to Ice and Bombs)

Hard Bloons:
Rainbow
Ceramic (Takes multiple hits to pop)

Boss Bloons:
MOAB (Mother Of All Bloons)
BFB (Big Flying Behemoth Spills out 3 MOAB's)

Step 4 Teh Monkeys

Dart Monkey
1st Weapon
Level 5 Upgrade: Spike-O-Pult
These guys are useless once you reach Round 10+ even with the Level 5 Upgrade it's still no good

Tack Shooter
2nd Weapon
Level 5 Upgrade: Ring Of Fire
This is a great weapon if you know where to place it it gets really powerful once you upgrade it to the Ring Of Fire ability

Boomerang thrower
3rd Weapon
Level 5 Upgrade: Lightsaber Thrower
This can really be a great weapon if a bloon manages to escape in the medium rounds. The lightsaber throw upgrade and pop at least 60 bloons in 1 throw.

Bomb Tower
4th Weapon
Level 5 Upgrade: MOAB/BFB Mauler
This is useful on the medium rounds but once you upgrade to the MOAB mauler rocket you can take down the MOAB in less than 7 shots (put up 5+ MOAB Maulers to own MOAB's faster)

Ice tower
5th Weapon
Level 5 Upgrade: Arctic Wind
this is like the tack shooter tower except it freezes the bloons. The arctic Wind upgrade is also simialr to the ring of fire it freezes a lot of bloons in the area and sometimes even pop them but overall it's not a good weapon against the hard section

Mortar tower
6th Weapon
Level 5 Upgrade: Mortar Battery
Not much to say about this tower it can pop 2 layers of bloons and the Mortar Battery upgrade triples your fire rate making it an effective weapon

Glue Gunner
7th Weapon
Level 5 Upgrade: Glue Splatter
This monkey won't really be useful until you get the glue splatter which effects 20 bloons in the area

Monkey Beacon
8th Weapon (Support Type)
Level 5 Weapon: Super Monkey Storm
The supportive stats aren't exactly helpful but the Super Monkey Storm can pack a punch if you're in a tight spot

Monkey Ace
9th Weapon
Level 5 Upgrade: Operation Dart Storm
This can be put anywhere around the map and if you have a lot of these and all of them have the Operation dart Storm upgrade you won't ever have to buy any pineapples

Monkey Buccaneer
10th Weapon
Level 5 Upgrade: Battleship
This won't really be of use until you upgrade it to Battleship which means non-stop shooting

Monkey Apprentice
11th Weapon
Level 5 Upgrade: Tempest Tornado
The Monkey Apprentice can both be helpful to you or maybe helpful to the bloons so upgrade this one carefully

Super Monkey
Ultimate Weapon
Level 5 Upgrade: ??? (Figure it out yourself! i'm not spoiling the ultimate weapon)
The super Monkey will shoot nonstop until those bloons are dead you can upgrade to the Laser vision and up to the Plasma vision and all the way to the really expensive ultimate upgrade...

Banana Farm
Money Increaser
Level 5 Upgrade: Banana Research Facility
Place these on spots you won't use then upgrade them for better money payout the sooner you get these in the easier for you to prepare for the harder rounds

Road Spikes
Trap
No Upgrade

Monkey Glue
Trap
No Upgrade

Pineapple
Trap
No Upgrade

Step 5 Streategies

Play on easy map on easy for full enjoyment
Play on an Expert map on hard if you're up for a challenge

Rounds 1-49 Rack Some Cash from some Noobs
Have at least 1 Super Monkey, 2 Level 2+ Banana Farms, 4+ MOAB/BFB Maulers, and 3 Mortars with the Mortar battery, and 2-3 Monkey Buccaneers Level 3+ BEFORE Round 50

Rounds 50-74 Dealing With The Bosses
Now that you've entered Round 50 you are now in MOAB territory use road spikes when needed and upgrade your banana farms when needed for better payout, buy more Mortars and Super Monkeys. Put the Super Monkeys' attack priority to "Strong" so in case an MOAB appears he'll shoot the MOAB more.

Rounds 75-99
By now, you should have 1 Glue Monkey (With Glue Splatter) 6+ MOAB Maulers, 4 Super Monkeys (2 with the ultimate upgrade), 7 Monkey Banana Research Facility, 6 Mortars With Mortar Battery, 5+ Monkey Aces with Level 5 Upgrade, and lotsa spikes in each level. Now first before you click start you MUST put the MOAB Maulers set on "Strong" mode or else the BFB's and MOAB's will escape easily. You are now in BFB territory now.

Rounds 100-149
I have yet to reach this round but have seen videos and there will be an amount of 50+ BFB's PER ROUND now good luck

Round 150
If someone eventually reaches or even beats this round you will be rewarded with an I.O.U. of an endless supply of Bananas...

Any Questions?

might update

[EDIT] looks like we have another troll on our hands who is it you may ask? ekim99 the butthurt noob the internet "tough" guy